Wind turbines are well known mechanical devices that have been used for hundreds of years to perform various types of mechanical work. In modern times the generation of electricity using wind turbines has developed into a large industry.
Referring to FIGS. 1-3, there is shown a traditional prior art turbine 10. Traditional turbines 10 have typically three rotor blades 12 fixedly mounted on a hub 14 rotating about a horizontal axis. The turbine is rotatably attached to a housing structure called the nacelle 15 which is located at the top of a high tower 16 in order to reach the stronger winds at higher altitudes. The nacelle 15 can rotate about the axis of the tower (the so-called yaw movement) in order to face the wind.
FIG. 3 is an expanded view of the nacelle and its internal components. The turbine typically rotates at low speed (about 10-15 rpm). This speed is typically too low to drive a conventional generator and therefore typically a gearbox 18 is inserted between the turbine and the generator 19, as shown in FIG. 3. Some modern turbines use a special generator that does not require a gearbox, a so-called direct drive generator. That is an attractive architecture in principle, because gearboxes are one of the most failure-prone components in turbines. However, direct drive generators are typically even larger, heavier and more expensive than conventional gearbox-driven generators, which renders this approach impractical in many cases, because modern turbines are already too top heavy.
The issue of excessive weight at the top of a very high and slender tower 16, generally over 100 meters, is one of the major problems in the wind industry. Weight impacts the cost of the tower, which has to be able to support the top-heavy architecture of the overall turbine system. This issue also impacts the cost and complexity of the components inside the nacelle 15, because they have to be designed to minimize weight and size, which leads to compromises that have caused widespread failures of gearboxes in the field.
Despite the efforts to design the components with minimum possible weight, the total weight of the nacelle has been escalating from about 100 tons in prior years to new levels approaching 500 tons in some cases because of the need to provide more power per turbine in order to make wind-generated electricity cost effective and competitive with fossil fuels.
With increasing weight, the cost of erecting a turbine has also increased because of the requirement to lift very heavy and bulky components to a high altitude and mount them on top of the tower 16. This task requires heavy duty cranes and similar equipment, which are not only very expensive, but are also very difficult to transport to the turbine site, further adding to the cost and complexity of manufacturing the turbine.
Another major issue with traditional wind turbines is the difficult and costly maintenance of the turbine. Maintenance personnel have to climb up extremely long ladders or have to be airlifted by helicopter to high altitudes under heavy wind conditions and often very low temperatures. Any significant repairs involving replacement of heavy components requires again bringing in the heavy cranes. Helicopters can be used in some instances, but this further increases the expense and risks. For off-shore turbines the difficulties are even further compounded. Some companies have built or are building special ships with giant cranes attached to them to be able to erect and maintain off-shore turbines, at extremely high expense. All these major difficulties at the end cause delays, downtime and invariably high expenses, which have to be passed on to the cost of wind-generated electricity.
The present invention addresses the above issues by removing the heavy components (transmission, generator, yaw motors, etc.) from the nacelle and relocating them at or near the bottom of the tower. The present invention provides a very innovative solution that makes it possible to locate the turbine at the high altitude required to take advantage of strong winds while at the same time providing a reliable and cost-effective approach.
The present invention seeks to overcome certain of these limitations and other drawbacks of the prior art, and to provide new features not heretofore available. A full discussion of the features and advantages of the present invention is deferred to the following detailed description, which proceeds with reference to the accompanying drawings.